Sound projector



K. WALTHER SOUND PROJECTOR Filed Jan. 9, 1963 March 29, 1966 INVENTOR. KLAUS WALTHER ATTORNEY United States Patent 3,243,766 SOUND PROJECTOR Klaus Walther, Detroit, Mich., assignor to The Bendix Corporation, Southfield, Mich., a corporation of Delaware Filed Jan. 9, 1963, Ser. No. 250,306

2 Claims. (Cl. 3408) This invention pertains to a sound projector and more particularly to an underwater sound projector having a plurality of discs along a central shaft which are in logarithmic periodic ratio and which provide a wider frequency band ratio than heretofore possible.

It is therefore an object of this invention to provide an underwater sound projector having an increased frequency band of operation.

It is a further object of this invention to provide such a sound projector utilizing an electromechanical transducer connected to a central shaft which is of increasing diameter and has a plurality of discs of increasing diameter and thickness which are spaced in increased gap lengths along said shaft. In the preferred embodiment, the shaft diameter, disc diameters, and thicknesses and gap lengths increase over the preceding corresponding measurement in the same ratio which may be 1.028.

These and other objects will become more apparent when a preferred embodiment is discussed in connection with the drawing which shows a plan view of a preferred embodiment.

In the drawing is shown an electromechanical device 20 which receives electrical energy such as a voltage of 28.3 v. R.M.S. from power source 22 and converts this energy to mechanical vibratory energy in tapered section 24. In this embodiment, electromechanical device 20 is a piezoelectric drive element of bariumtitanate cylinder of one inch length, one half inch outside diameter, and one eighth inch wall thickness. With vacuum loading, this element has a longitudinal resonance frequency of one hundred kilocycles. In order to achieve large electromechanical band widths, it is desirable to load the drive 20 with a material, the mechanical wave impedance of which is equal to that of the transducer material (W. Roth, Piezoelectric Transducers, Proc. IRE, vol. 37, p. 750 (1949)). A bariumtitanate transducer operating into a brass load satisfies the condition. By scaling the mechanical dimensions, the operating frequency can be changed to any desired range. Other suitable electromechanical transducers such as magnetostrictive, may be utilized as drive elements. Also, several different e'lectromechanical transducers may be stacked together which are designed to resonate at different frequencies to increase the overall output band width of the sound propector principle of the distributed transducer, (M. Greenspan and R. M. Wilmotte, Distributed Transducers, Iourn. Acoust. Soc. of America, vol. 30, p. 528 (1958)). In the case of multi-transducers the transducers Will be activated in phased sequence.

Tapered or conical section 24 is the first portion of a one piece machined brass logarithmic-periodic sound projector antenna assembly. The other elements of the antenna include a plurality of discs 1, nl, n, n+1, n+2, N1 and N. All of these discs are connected together and spaced apart from one another by a central shaft 26. In the preferred embodiment, there are 61 such discs.

In this invention, the thickness t of any disc n, is related to the thickness t of the succeeding disc n+1, by the same ratio that the diameter D of the disc n is to the diameter D of the disc n+1. Also, the gap g between disc n and disc n+1 is related to the succeeding gap g by the aforementioned ratio as is the diameter d Patented MaruZQ, 1966 of shaft 26 related to the diameter d Stated in equation form,

;*i= /16; 3 and %:'J=/4 for D equal to or greater than /2 inch and a,, is equal to .125 inch for D equal to or less than inch.

In the preferred embodiment there are 61 elements or discs to provide a projector having substantially constant acoustical power output over a frequency range of band width ratio of 3.4 to 1 with a single drive element. In this embodiment the frequency range in which the acoustical power output stayed within plus or minus 1.5 decibels covered from 38.2 to kilocycles. An electroacoustical efficiency larger than 60 percent was obtained in this frequency range. This is an additional advantage of this transducer design, because conventional transducers show a decrease of efficiency with increasing band width.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described my invention, I claim:

1. Apparatus comprising electromechanical means for transforming electrical input to mechanical vibrations,

means for changing the mechanical vibrations to acoustical vibrations comprising,

a center shaft of increasing diameter with the smaller end of the shaft being connected to said electromechanical means for transforming electrical input to mechanical vibrations,

a plurality of discs fixed at their centers to said center shaft and spaced along said shaft,

said discs being of increasing diameter as the distance from said electromechanical means increases,

the axial thickness of said discs increasing as the disc diameter increases,

the longitudinal gap between successive discs increasing as the disc diameter increases,

the ratio of each disc thickness and diameter to each succeeding disc thickness and diameter respectively being substantially a constant having a value between 1 and 1.033,

the longitudinal gaps between discs increasing at a substantially constant ratio of between 1 and 1.033 with any gap nearer said electromechanical means being smaller than any gap farther away from said electromechanical means,

the shaft diameter at successive gaps increasing at a substantially constant ratio of between 1 and 1.033 with any shaft diameter nearer said electromechanical means being smaller than any shaft diameter farther away from said electromechanical means with said shaft diameters being larger than a predetermined minimum,

said shaft diameters, disc diameters, disc thicknesses,

and gap lengths thus being proportioned to effectively radiate and receive a frequency range having a band width where the high frequency is in the order of 3.4 times the low frequency with a power varia- 3 tion within plus or minus 1.5 decibels over said band width.

2. The apparatus of claim 1 with said gap length being equal to approximately of a smaller of the two disc diameters which define the boundaries of the gap length,

the axial thickness of any disc being equal to approximately V of a diameter of the disc,

and the diameter of the shaft being equal to approximately /1 of the nearest disc diameter for discs larger than /2 inch in diameter and the diameter of the shaft being equal to approximately /8 inch between all discs smaller than /2 inch diameter.

References Cited by the Examiner UNITED STATES PATENTS 7/1928 Harrison 3408 11/1933 AlIel 34016 

1. APPARATUS COMPRISING ELECTROMECHANICAL MEANS FOR TRANSFORMING ELECTRICAL INPUT TO MECHANICAL VIBRATIONS, MEANS FOR CHANGING THE MECHANICAL VIBRATIONS TO ACOUSTICAL VIBRATIONS COMPRISING, A CENTER SHAFT OF INCREASING DIAMETER WITH THE SMALLER END OF THE SHAFT BEING CONNECTED TO SAID ELECTROMECHANICAL MEANS FOR TRANSFORMING ELECTRICAL INPUT TO MECHANICAL VIBRATIONS, A PLURALITY OF DISCS FIXED AT THEIR CENTERS TO SAID CENTER SHAFT AND SPACED ALONG SAID SHAFT, SAID DISCS BEING OF INCREASING DIAMETER AS THE DISTANCE FROM SAID ELECTROMECHANICAL MEANS INCREASES, THE AXIAL THICKNESS OF SAID DISCS INCREASING AS THE DISC DIAMETER INCREASES, THE LONGITUDINAL GAP BETWEEN SUCCESSIVE DISCS INCREASING AS THE DISC DIAMETER INCREASES, THE RATIO OF EACH DISC THICKNESS AND DIAMETER TO EACH SUCCEEDING DISC THICKNESS AND DIAMETER RESPECTIVELY BEING SUBSTANTIALLY A CONSTANT HAVING A VALUE BETWEEN 1 AND 1.033, THE LONGITUDINAL GAPS BETWEEN DISCS INCREASING AT A SUBSTANTIALLY CONSTANT RATIO OF BETWEEN 1 AND 1.033 